The present invention relates to the papermaking arts including fabrics and belts used in the forming, pressing, and drying sections of a paper machine, and to industrial process fabrics and belts, TAD fabrics, engineered fabrics and belts, along with corrugator belts generally.
The fabrics and belts referred to herein may include those also used in the production of, among other things, wetlaid products such as paper and paper board, and sanitary tissue and towel products made by through-air drying processes; corrugator belts used to manufacture corrugated paper board and engineered fabrics used in the production of wetlaid and drylaid pulp; in processes related to papermaking such as those using sludge filters and chemiwashers; and in the production of nonwovens produced by hydroentangling (wet process), meltblowing, spunbonding, airlaid or needle punching. Such fabrics and belts include, but are not limited to: embossing, conveying, and support fabrics and belts used in processes for producing nonwovens; filtration fabrics and filtration cloths; and fabrics and belts used for textile finishing processes such as calendering and hide tanning.
Such belts and fabrics are subject to a wide variety of conditions for which functional characteristics need to be accounted. For example, during the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
It should be appreciated that these industrial fabrics such as paper machine clothing (PMC) such as the forming fabrics, press fabrics, and dryer fabrics, all take the form of endless loops on the paper machine and function in the manner of conveyers.
Such fabric structures are typically constructed from synthetic fibers and yarns, which may be monofilaments or yarns made with more than one filament plied and/or ply/twisted together, by conventional textile processing methods such as weaving, for example. Yarns may also be knitted or braided. It is often desirable to selectively tailor the fabric structure to affect or enhance a performance characteristic important to, for example, the papermaker, such as fabric life, sheet formation, runnability or paper properties.
Many of these fabrics are on machine seamable i.e., the fabric can be woven according to the desired dimensions and can be mounted on the machine so that the cross machine direction (“CD”) edges of the fabric may be seamed on the paper machine itself. In case of press fabrics, this is typically carried out by interdigitating seaming loops formed by machine direction (“MD”) yarns on the CD edges of the fabric and inserting a pintle into the channel formed by the interdigitated seaming loops. One method of making on machine seamable fabrics is referred to as “modified endless weaving,” where the fabric is woven in a continuous loops and modified to take an on machine seamable form. In such a fabric, the warp yarns lie in the cross machine direction and the weft yarns lie in the machine direction. After the fabric is woven on the loom, the widthwise edges or CD edges of the fabric are brought together on the paper machine and the MD seam loops formed by the weft yarns are interdigitated, and the two edges are seamed by inserting a pintle into the channel formed by the interdigitated seam loops.
Another method is to produce a woven in loop seam or pin seam by flat weaving a fabric, raveling out some of the CD yarns, and weaving back in the MD yarns to form loops on each fabric edge. The loops can be interdigitated and the fabric can be seamed as discussed above. A third method is to produce a nonwoven fabric structure using an MD yarn array that forms the seaming loops. In this method, one or more layers of a single yarn are wound around two parallel rolls that are spaced apart. The yarn is wound in a spiral manner (yarns are at a slight angle to the MD of the final fabric) until a desired width of the fabric is reached. The distance between the rolls can be varied depending on the required MD length of the fabric in use. Similar methods and fabrics are disclosed, for example, in commonly owned U.S. Pat. No. 6,491,794 to Davenport and U.S. Patent Application Publication No. 2005/0102763 to Eagles, the entire contents of which are incorporated herein by reference
Yet another method of making on machine seamable fabrics is to produce a seamed multiaxial fabric, such as that disclosed in commonly owned U.S. Pat. No. 5,939,176 to Yook, the entire contents of which is incorporated herein by reference.
In some fabrics, textile ply/twisted yarns or yarns with more than one strand or filament are used in the MD rather than a single monofilament. This is particularly necessary in nonwoven arrays when the anchoring of the MD yarns by the CD yarns does not occur. Such multistrand yarns provide for improved elasticity and strength and are an answer to the tensile and fatigue problems of a single monofilament. However, when one attempts to form the loops for a “pin seam” from these MD yarns, serious problems are encountered. The loops so formed have the tendency to deform at the apex or to lose their relative parallelism. In addition, the entire loop will rather easily deform or bend as one attempts to interdigitated the loops and/or force a pintle through the channel formed by the interdigitated loops.
Another problem arises as a result of a phenomenon called the secondary helix effect. Ideally, the pin seam loops will be properly oriented when their planes are perpendicular to the plane of the fabric and parallel to the machine direction. Such an orientation makes it possible for the loops at each end of the fabric to be interdigitated and alternated easily during the joining of the ends to form a pin seam. The secondary helix effect is observed in the tendency of a loop 10 formed from a ply/twisted yarn 12 having more than one strand to turn about an axis lying in the plane of the loop, such as that shown in FIG. 1. When this occurs, it represents a departure of the loop from the ideal orientation needed to form the pin seam. Such departure makes it difficult, if not impossible, to properly interdigitate and alternate the loops on each end of the fabric during closure, as well as to force the pintle through the void created by the interdigitated loops. Typically, the orientation of the seam loops 10 is maintained until installation using a stabilizing element 16, for example, a spiral coil, such as that disclosed in commonly owned U.S. Pat. No. 7,393,434 to Kornett, and shown in FIG. 2. However, once the stabilizing element is removed for installation of the fabric, the seam loops loose their orientation due to the secondary helix effect. Therefore, any on machine seamable fabric formed of ply/twisted yarns with more than one strand will have issues with loop alignment and orientation/parallelism.